Storage

Cookies

Servers can set cookies using the HTTP Set-Cookie header. JavaScript cannot read that header. [MDN]

document.cookies is used to read or write cookies from the client-side [MDN].

Some users may have completely disabled cookies. In some browsers, this may break other (unrelated) APIs. [blog.tomayac.com]

IndexedDB is a way for you to persistently store data inside a user's browser. Because it lets you create web applications with rich query abilities regardless of network availability, these applications can work both online and offline. IndexedDB is useful for applications that store a large amount of data (for example, a catalog of DVDs in a lending library) and applications that don't need persistent internet connectivity to work (for example, mail clients, to-do lists, and notepads). [MDN, MDN, MDN, caniuse]

Browsers may have different storage and retention limits [MDN, MDN, web.dev].